The invention pertains to the field of hydraulic systems utilizing flexible hose conduits interconnecting the components of the system.
Pressurized fluid systems commonly employ a fluid reservoir, a pressure producing member, such as a pump, pressurized fluid utilizing means, such as a rotary hydraulic motor, an expansible chamber motor or a bearing, and valve components are usually used for controlling the flow of medium between a pump and motor. Hydraulic pressurized systems are employed in a wide variety of environments wherein pressurized fluid is used to lift, lower, push, pull and position components relative to each other. Also, similar systems are used for lubrication purposes, such as in internal combustion engines and heavy duty equipment utilizing pressurized bearings.
In the pumping of the fluid, the valving and the fluid flow, considerable heat is generated within the fluid due to shear forces, and as the pressurized medium utilizing means, such as the motor, may be mounted upon a component movable with respect to the valve or pump, flexible hose lines are often commonly employed between the various components of the system. The combination of high internal hose pressure, heat and flexing cause the hose to deteriorate and periodic replacement is required.
Another detrimental effect upon flexible hose as used in pressurized hydraulic systems lies in the "aging" that occurs as the hose is stored, or while in use. Such aging results from oxidation and the effects of Ozone and the other agents present in the air, particularly at industrial locations.
Also, the hose employed in pressurized hydraulic systems is subjected to possible chemical reaction with the fluid itself and it is necessary that the hose material be chemically compatible with the hydraulic fluid being employed. For instance, certain fire resistant synthetic hydraulic fluids require a different type of hose material than more conventional petroleum based hydraulic fluids.
In the past, it has been necessary for pressurized hose distributors to maintain a large inventory of hose to meet the requirements of usage, and as hydraulic hose is manufactured in a wide range of sizes and to meet a wide variety of pressure specifications, the hose inventory requirements of a hose distributor become very large and costly.
In an effort to meet the aforementioned problems with respect to improving the life and operating characteristics of pressurized flexible hose, a number of hose elastomers and rubbers have been used, such as Buna-N rubber, ethylene propolyene rubber, butyl rubber and polychloroprene rubber. However, while certain of such elastomers and rubbers are usable with petroleum based fluids and others are usable only with non-petroleum based fluids, these elastomers age on the shelf and in use, are not usable with a wide range of fluids of various chemical composition, and rapidly deteriorate at elevated temperatures, such as 300.degree. F., and are usable only at relatively low temperatures. Under hydraulic impulse tests wherein hydraulic pressures are imposed upon a test hose periodically under controlled temperature conditions, hoses from such materials, though reinforced, usually fail at less than 200,000 pressure impulse cycles, and under flexing-pressurization tests at 300.degree. F. such hoses usually fail at less than 300,000 cycles and 300 hours of testing. It will therefore be appreciated that under relatively high temperature conditions such pressurized flexible hose having working pressures between 500 and 3,000 psi must be replaced relatively often.
It has been recognized in U.S. Pat. No. 3,528,260 that a flexible hose using cross-linked chlorinated polyethylene as a major constituent is of advantage as used in refrigeration systems employing Freon type refrigerant fluids. However, the hose disclosed in this patent is not suitable for use with most hydraulic pressurized fluid applications as it would not withstand the elevated temperatures of such usage, and would also fail due to the higher pressures encountered as compared with a refrigeration circuit.